Abstract
The preparation and characterization of novel carboxyl-containing polyimide (PID) grafting sulfonated polyvinyl alcohol (SPVA) copolymer membranes applied in vanadium redox flow batteries (VRFBs) are presented in this work. The microphase structures of the copolymer membranes are identified by TEM and XRD. Other basic properties are characterized, particularly the oxidative and water stability. The copolymer membranes exhibit better chemical stability than normal SPIs with five-numbered rings due to the covalent bonds between PI and SPVA as well as highly dispersed microphase separated structure. The physico-chemical properties of the copolymer membranes, including IEC, water uptake, swelling ratio, proton conductivity and vanadium ion permeability are evaluated and compared with Nafion 117. The PID30-g-SPVA membrane has the highest proton selectivity (1.33 × 105 S min cm−3), being much higher than that of Nafion 117 (0.41 × 105 S min cm−3). In VRFB single cell tests, the cells assembled with copolymer membranes show higher coulombic efficiency (CE), higher energy efficiency (63.3% vs 74.3% at 90 mA cm−2) and much lower self-discharge rate than with Nafion 117. In addition, the copolymer membranes retain excellent stability after 100 cycles. All the results show that the copolymer membranes have promising prospects for VRFB applications.
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